1. Field of the Invention
This invention relates to pulley mechanisms for lifting loads and in particular to a pulley mechanism that as the load is lifted and a pause is made between the lower and the upper lifting limits, a pawl engages the rope or cable to hold the load in place while there is no lifting force at work.
In most cases such pawl arrangements must be manually disengaged to release the load, but in the present case there is provided a mechanism for automatically releasing the pawl lock when it reaches a predetermined height, and, in a similar manner, to automatically reset the engaging mechanism when the lifting line reaches a certain predetermined position.
2. Prior Art
U.S. Pat. No. 1,389,514 Kestell discloses an automatic locking pulley with a housing. The pulley is mounted on a supporting lever which is fulcrumed at its lower portion and can be tilted outside the housing in an opening. The pulley revolves on a pintle and the rope is trained over the pulley. The lower end of the supporting lever is angled and serrated with teeth.
In this case either the rope on the load side or the pulling side must be pulled to the side and a lever tilted to the side, locking the rope or releasing the rope to let the load down. The changing from locking to release and vise versa is accomplished by side pulls on the ends of the rope that is either pulling or loaded.
U.S. Pat. No. 2,608,174 Sponenburg discloses an adjustable safety device for a boat anchor with an automatic locking member engaging the rope to prevent it moving downward. If an adjustment is necessary the rope is pulled to the side and moves within a recess in the locking member.
Various other disclosures of rope or cable clamps in combination with pulleys are shown in the following references:
______________________________________ U.S. Pat. No. 1,107,934 Hagan U.S. Pat. No. 4,097,023 Muller U.S. Pat. No. 1,167,295 Hall U.S. Pat. No. 4,502,668 Dodge, Jr. U.S. Pat. No. 2,867,875 Davison U.S. Pat. No. 5,521,000 Dodge, Jr. U.S. Pat. No. 4,542,884 Dodge, Jr. ______________________________________
None of the foregoing references are structurally similar to the device of the present invention or accomplish the end goals in the same manner nor as efficiently.